1. Field of the Invention
The present invention relates to an electric rotary machine having cooling fins for cooling a stator coil, and more particularly to an alternator for use in an automotive vehicle in which cooling fins are disposed in contact with a stator coil to effectively cool down the stator coil.
2. Description of Related Art
An alternator which is a kind of an electric rotary machine that may be used in an automotive vehicle to generate electric power for charging a battery and supplying electric power to various electric devices such as lighting equipment, an ignition system and others. Recently, more electric power is being required for a vehicle because the number of electric devices including electronic control systems used in a vehicle is increasing, and a mounting space for the alternator is getting smaller. Therefore, it is required that the alternator generate high power with a compact size. High efficiency and compactness of the alternator is also required from a standpoint of fuel economy.
It is generally known that it is effective, for attaining a higher efficiency of an alternator, to reduce copper loss generated in a stator coil (I.sup.2 R, where I is stator current and R is resistance of the coil). Since the stator coil resistance is dependent on temperature of the coil and increases with temperature rise in the coil, the temperature rise in the coil has to be suppressed by cooling down the coil.
A conventional technology for cooling down the stator coil is disclosed, for example, in Japanese Patent Laid-Open Publication No. Hei-6-70508. An electric rotary machine disclosed in this publication has a metal ring attached to a coil end for cooling the coil by conducting heat generated in the coil to the metal ring and a housing. The metal ring is attached to the coil end by an adhesive tape and a filler material. Another conventional technology is disclosed in Japanese Utility Model Laid-Open Publication No. Hei-1-166477and Japanese Patent Laid-Open Publication No. Sho-63-213464. A linear motor disclosed therein has a resin-molded coil on which a heat radiating fin is formed. The coil is cooled down by the radiating fin.
Since the coil of the electric rotary machine disclosed in the publication Hei-6-70508 is cooled down by heat conduction through the adhesive tape and the filling material, cooling efficiency is not high enough to apply this technology to a coil of an alternator for use in a vehicle generating continuously a large amount of heat. The coil of the linear motor disclosed in the publication Hei-1-166477 or Sho-63-213464 is cooled by natural radiation from the radiating fin formed on the resin-molded coil. Therefore, cooling efficiency is not high enough to apply the same technology to an alternator.